Kurt Julian Weill (March 2, 1900 – April 3, 1950) was a German composer, active from the 1920s, and in his later years in the United States. He was a leading composer for the stage who was best known for his fruitful collaborations with Bertolt Brecht. With Brecht, he developed productions such as his most well known work The Threepenny Opera, a Marxist critique of capitalism, which included the ballad "Mack the Knife". Weill was a socialist who held the ideal of writing music that served a socially useful purpose. He also wrote a number of works for the concert hall, as well as several Judaism-themed pieces.